Worms

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Acoelomate

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A term used to describe organisms that lack a body cavity (coelom) between the digestive tract and the outer body wall.

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Cephalization

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The evolutionary trend where sensory organs and nervous tissue become concentrated at the anterior end of an organism, leading to the formation of a head.

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Bilateral Symmetry

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A body plan in which the left and right sides of an organism are mirror images of each other.

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Turbellaria

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A class of flatworms that are mostly free-living and found in aquatic environments.

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Annelids

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A phylum of segmented worms that includes earthworms, leeches, and marine worms.

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Hirudinea

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The class of annelids that includes leeches, characterized by a flattened body and the presence of suckers.

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Oligochaeta

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A class of annelids that includes earthworms, characterized by a segmented body and few setae (bristles).

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Polychaeta

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A class of annelids that includes marine worms, characterized by many bristles (setae) and often a well-developed head.

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Gastrula

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An early embryonic stage that follows the blastula, characterized by the formation of the three germ layers: ectoderm, mesoderm, and endoderm.

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Earthworms

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A type of oligochaete annelid that plays a crucial role in soil aeration and nutrient cycling.